let arr = ['a','b','c','d','e']

/* arr.map((item,index,arr)=>{
    arr[index]=item+'1'
})
console.log(arr);
 */
Array.prototype.my_map = function(fc){
    const newArr =[]
    for(let i =0;i<this.length;i++){
        const res= fc(this[i],i,this)
        newArr.push(res)
    }
    return newArr
}